Cannot offset: unvalid curve

I have a relatively simple closed curve which is a part of a Chinese character originated from a TTF. I want to create an offset on the inside of that curve, but when I do that Rhino3D says ‘Selected curve is invalid’. I have isolated this curve and uploaded it here:Offset_unvalid curve.3dm (30.9 KB)
What is wrong with this curve?

Hi Hans - font curves tend not to be very good in general - this one is worse than most I guess. I’ll see if I can get it working…

@Hans2 for now, try ConvertToBeziers > DeleteInput=Yes, then Join the results.

Pascal

I just followed your instruction and that did solve it for me. Thanks a lot for the tip.

Hans.